Some people already submitted this news last week, but it wasn't until today that it became official: the FreeBSD team has announced the release of FreeBSD version 9.0. As you may expect from the major version number change, this is releas eis packed with new stuff.

A Red Hat EL 6 clone like CentOS or Scientific Linux would be a good fit. Not to go back three years, Read: you should install the latest, but it will be supported until at least 2017 and would be good enough for people who don't need bleeding edge.
After all, once the media player has been fed with all necessary codecs you only need to update from the repos.

That should be long enough, and you can probably long before that sell them a machine with 7 on it.

It would be up to you as the reseller to enable additional media repos and set up the desktop a bit nice, with a shiny wallpaper maybe, and once your GOLD image is done you're good for a while, maybe spinning a new one for updates from time to time.